Separable connector for high frequency coaxial cables



Jan. 29, 1963 P. EDELMAN 3,076,158

SEPARABLE CONNECTOR FOR HIGH FREQUENCY COAXIAL CABLES Filed Feb. 9, 1959 2a J|Y V 4 Fm] 2 F 6A 3 m 23A 4 I7 BF 27- ,4 IO \7 26G 5 c 26,; .1 2s 'A 26 FIG. I. 26K

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. PHILIP EDELMAN ATTORNEY.

P. EDELMAN 3,076,158 SEPARABLE CONNECTOR FOR HIGH FREQUENCY COAXIAL CABLES Jan. 255, 1963 2 Sheets-Sheet 2 Filed Feb. 9, 1959 INVENTOR. PHILIP EDELMAN United States Patent FOR HIGH CABLES This invention relates to a tightly sealed but separable connector that is suitable for a broadband high frequency coaxial cable line; also, more particularly, to a hermetically sealed cable extension or connector for use With a subminiature radio frequency transmission line of an electronic system for typical uses, as in radar or pulse-Wave transmission.

nectors, with a minimized standing wave ratio, while the attenuation loss, under widely varying ambient operating conditions, is also kept at a minimum value for each operating frequency.

A further object is to afford a high insulation breakmg large ambient temperature changes.

A further object is to simplify the necessary manipulations and labor required in attaching the connector on the cut cable.

A further object is to reduce transmission losses through the connector.

A further object is to provide a clamping means that gathers and bunches the loose ends of the outer conductor of the cut coaxial cable to facilitate its attachment into the connector.

A coaxial line and especially a sub-miniature coaxial large transmission surface. the enveloping capacitance dielectric.

The strict requirement of FIGURE 3 shows a modified partly sectioned enlarged vieW of a modified form of connector having fewer parts than the preferred embodiment illustrated in FIGURE 2.

In FIGURE 1 there is shown a cut operating length of a typical sub-miniature coaxial cable 1, such as, for example, military No. R.G/ 188-U, which has a rated characteristic surge impedance of 50 ohms. cable 1 is approximately described as having an inner tially 2.1, but different temperatures. The Wall thickness presents a dielectric strength of 2,000 volts (R.M.S.) derated for corona limit to 1,200 volts. This cable is covered over its outer conductor by a flexible plastic jacket of 0.10 inch diameter. Whenever a sub-miniature single coaxial line 5 is connected into an electronic system, troublesome problems occur that are particularly due to of the cable. Unsatisfactory methods for cutting, stripping, binding, and fastening the cables conductors and insulation cause failures during the subsequent usage.

Ideally, a sharply cut cable should be restored in exact diametrical ratios of its own inner and outer conductors ly crimped fastenings tended to deform the coaxial cable The present invention of such problems. More particularly, the unsatisfactory voltage breakleaking spaces at the junction of insulating members that support the extension conductors of the connector. This circumstance greatly increases at a high altitude ambient condition where the breakdown voltage is only a small fraction of its value at sea level. The high altitude promotes ionization, corona, and leads to actual arcing or breakdown at only a fraction of the voltage required for breakdown at sea level. The voltage breakdown is also accelerated at elevated temperatures which affect the dielectric strength at all pressures. The present invention provides a reliable tight seal for the connecting conductors which remains eifective at all altitudes.

The large resistivity of a miniature inner or center conductor to radio frequency current arises from the skin effect. The current density is not uniform but is crowded within a very thin layer on the small sized conductor.

'A standing wave forms from the additfon of reflected to directly traversing waves. The combined voltage presents a max mum at particular points on the line which appear one-ha.f wave length apart. The combined voltage becomes a minimum value at intermediate points spaced one quarter wave length away. At these quarter wave length points the combined voltage is the difference of the direct and the reflected wave at that minimum point. According to the disclosed invention, certain novel combinations of short discretely different transmission characteristics are inserted in a compensating sequence within the connector set 2 to offset discontinuity at a cut end of cable 1. A short axial increment which has a length shorter than its diameter is placed adjacent to another short transmission length in the connector set 2 to define a d-iflerent diametrical ratio. The combined sequence of these increments is found to smooth out the overall transmission characteristic via the connector set 2 that includes this novel compensation. A preferred form of the invention includes flexible capacitance dielectrics that are compressed to define different diameters for this purpose. 7

A cut coaxial cable 1 with its extending connectors 2 comprises a transmission line 5 that can convey radio frequency energy or information signals. When this line is included in an electronic system it may be required to handle a broad band of frequencies without detrimental discrimination and at a minimized loss. This loss is enhanced wheneverthe connectors present uncompensated discontinuities that deviate from the uniform characteristic line impedance to cause a high value of voltage standing wave ratio (V.S.W.R.). This is a ratio that can be measured to show the quality of the connectors toward minimizing the effect of reflected waves that add to the direct- 1y traversing waves in the form of standing waves. The V.S.W.R. cannot be less than unity but may be any higher whole or fractionally mixed number. In the vicinity of unity (1) there is a negligibly small reflected Power loss, but in the vicinity of two (2) ten percent of the power becomes reflected, (0.5 db loss), and at a V.S.W.R. of three (3) this increases to a twenty-five percent power reflection.

- A sub-miniature coaxial line 5, as in FIGURE 1, has small transverse dimensions which limit its power handling level to related small values. Its minimized cross-sectional dimensions nevertheless permit the transmission of very high frequencies extending upwards until the wave length is not large compared to the cables cross-section. The attenuation loss, inherent in the sub-miniature cable, restricts the length of coaxial cable that can be practically utilized as the upper frequency limit is approached. Near this upper frequency limit, the extension connectors for the coaxial cable must also have a cross-sectional diameter that is only a small fraction of the highest wave length that is to be accommodated.

Since the entire sub-miniature transmisison line 5, inclusive of its coaxial cable 1 and the extending cable connectors 2, should present uniform continuity from one end to the other and because this is not feasible along the axial length of the connectors, the present invention provides simulated uniformity by means of very small compensating sections within the connectors. Since the line serves to transmit two waves, one direct and the other reflected, simultaneously in opposite directions and because multiple waves can propagate along the line, a preferred form of this invention provides a reciprocally symmetric continuity about the middle of the assembled line. With this symmetric continuity as either of the two ends along the axis of the connectors is approached from the middle of the cable, each incremental length of changed diametrical ratio nearing one end is balanced by an identically changing ratio nearing the other end. This simulates an equivalent smoothly symmetrical distribution of tiny increments extending the outer and inner line conductors in a sequence of stepped diametrical ratios. The diameters at the junctions for the compenzating increments are abruptly changed so that adjacent very short axial distances present different impedances. This affords a substantially constant time delay for all of a broad range of frequencies so that pulsed waves can be propagated at modulated radio frequencies without distortion.

The cable 1, as shown in FIGURE 1, has its two ends cut and attached to a pair of similar separable connector sets 2 to form a removable single coaxial transmission line 5 having terminations 3. The connector sets 2 are attached to the coaxial cabe ends in a reciprocal symmetry, that is electrically balanced about the cables mid length point 1 All of the combined elements that are shown in either FIGURE 2 or in FIGURE 3 thus individually have a reversible complementary position with respect to point 1 The assemblies at terminations 3 are interchangeable.

The cable 1 with its extending connectors 2 affords a transmission line that can convey radio frequency energy as waves traversing the length in either direction. The line 5 is included in an electronic system, that is typically shown in FIGURE 1, by sealing receptacles 4 of the connector sets 2 to suitable electronic units 6 and 7 at their respective bulkheads 6 and 7 to afford a reliable interconnection of the operating units 6 and 7 with a minimum of attenuation and reflected power loss. The line 5 may also be quickly disconnected at either or both endsfor reconnection to other units that replace the units 6 or 7.

A cross-section of a preferred embodiment of a connector according to the invention is shown in FIGURE 2. Cable 1 is cut to expose a short end of its center conductor 1 and a short length of its outer conductor 1;; is severed so its end is spaced away from 1 to leave an exposed length of thecapacitance dielectric I as indicated. In assembling the illustrated connector a bend-relieving boot or sleeve 17, preferably of silicone rubber, is first slipped over the cables jacket 1 and is subsequently assembled over the fastener 18, as shown. slipped over the jacket 1 and is subsequently assembled as shown. Fastener 18 defines a closely fitting bore 18 near one end to hold the cables jacket 1 and also defines a concentric bore 18 which is tapered from its other end to receive and grip a tapered clamp ring 19. Fastener 18 is externally threaded at 18 and has a flattened flange 18;; to facilitate assembly,

Metallic clamp ring 19 has a preferably slit bore 19 to grip the cable jacket 1 and also has a sequence of concentrically stepped smaller bores 19;; and 19 When the bore 19 is slid over the jacket 1 the cut loose ends of the cables outer conductor 1 are gathered, stripped away from the cables capacitance dielectrio 1;, against the abutment between the bores 19 and 19 and become bunched in the bore 19 between the cut end of the cable's jacket 1 and the shoulder end of the smallest bore 19 This combined stripping and bunching permits the clamp ring 19 to grip and contact against the gathered and bunched outer conductor 1 Optionally, the clamp ring 19 may also be soldered to the bunched outer conductor 1 The smallest bore 19 Fastener 18 is initially V serves to strip the loose cut ends of the outer conductor 1 away from the exposed capacitance dielectric 1 This stripped or exposed length I of the dielectric is preferably at least as long as the diameter of the capacitance dielectric, to afford an enlarged creepage path between the conductor ends 1 and 1;; that is several times the radial distance between 1 and 1 Members 18 and 19 are preferably plated to afford corrosion resistance and good electrically conductive surfaces. As the tapered periphery 19;; of the clamp ring 19 enters the coacting bore 18;; defined in the fastener 18, the jacket end 1 and the bunched conductor end 1 subsequently become clamped by the ring 19 and held by the fastener 18, but the cable 1 does not become indented nor irregularly deformed.

A rotatable captive nut 21, of any suitable material, is preferably knurled at 21 and is internally threaded at 21 The nut 21 also has an annular captive end 21 This end 21 after assembly as shown, is rotatable but is axially held captive against either the flange 18 of the fastener 18 or the end 8 of an annular shell 8. Shell 8 has an internally threaded end 8 which engages a complementary part of fastener 18. The hollow nut 21 serves to draw the plug assembly 3 and the socket assembly 4 together when the end 23 of nut 21 is forced against end 8 of shell 8. Nut 21 also serves to force plug assembly 3 away from assembly 4 when end 21 is forced against the flange 18 of fastener 18. This gradual threaded engagement and disengagement relieves stresses on the small inner conductor 1 so that it is not damaged.

An inner contactor 10, metal, is attached or soldered to the exposed end of the cables inner conductor 1 and serves as an electrical extension for 1 Solder 23 of 60/40 tin and lead composition is suitable and may be preferred.

As above described, the cut cable 1 has been provided with a flexible bend relief sleeve 17, an extension contactor 10 attached to the end of its inner conductor 1 and a clamp ring 19 fastened to its bunched outer conductor 1 and to the uncut end of the cables jacket 1 The fastener 18 also serves to hold the jacket 1 one end of the sleeve 17 and to engage and hold the clamp ring 19. The aforesaid sub-assembly combination affords a means to mechanically fasten and electrically extend a cut end of the cable 1 whereby an enlarged electrical creep distance separates the extended end of the cables inner conductor 1 and the gathered loose ends of its outer conductor 1 that are bunched and fastened in the ring 19 Annular shell 8 functions to extend the cables outer conductor 1;; via the ring 19 and the fastener 18 when the threads 18 engage the mating threads 8 so that the shell is electrically connected as an extension of the cables outer conductor 1 Shell 8 is of a suitable metal that is compression bondable and hermetically sealable to a fused inorganic or glass seal 24. The metal may be #B-lll3 steel, of commerce, that is subsequently suitably plated to afford corrosion resistance and good electrically conductive surfaces. The dielectric glass 24 may be #9010 Dow-Corning compression sealing glass, of commerce.

Dielectric annulus 24 is positioned intermediate the ends of shell 8 within a bore 8.; as shown; Annulus 24 is thus bonded Within the plug. 3. Glass annulus 24 is also compression bonded and hermetically sealed upon a guide ring 25. Ring 25, of a suitable alloy such as commercial #52 Driver-Harris nickel alloy, is concentrically aligned within the annular shell 8 so that the ends of ring 25 protrude a limited distance beyond the substantially parallel flattened end surfaces of the sealing annulus 24. This limited axial distance from each surface of the seal 24 is preferably less, but not more than, onethird of the thickness of the annulus 24. Annulus 24 is'preferably made as thin as is compatible with good mechanical strength and acurate sealing, diameters proportioned as indicated. These diameters are related to transmission wave lengths and are all specified to be so small as to be a very small fraction of the shortest wave length that is to be transmitted. Hermetically sealed ring 25 has internally chambered or countersunk ends to facilitate positioning of contactor 10. Contactor 10 preferably is provided with shoulder 10,, for abutment against ring 25, and may also be soldered to ring 25.

Shell 8 is tapered externally as indicated at 8;; so as to concentrically align and engage into the receptacle 4 without detrimental electrical contact noise. Guide ring 25 and shell 8 are suitably surface-plated for corrosion protection and for good electrical conductivity, after the bonding with the insulating glass 24.

A pre-stressed combined flexible capacitance elastomer and compression sealant annulus 22 is placed in shell 8 and and of length and that of the cables stripped dielectric I It is also defined with a large outside diameter than that of the bore 8;; in the shell 8 and is pressed into this bore so as to be prestressed. The annulus also defines a free length that is larger than the compressed length as shown in FIGURE 2. FIGURE 2 shows the elastomer 22 after it has been placed under compression by tightening fastener 18 relative to shell 8 via the engaged threaded ends 18 and 8 Before assembling shell 8 with fastener 18, nut 21 is placed over To facilitate the engagement of fastener temporarily threaded upon a receptacle 4 to draw its tape-red end 8;; into and against this receptacle. This permits The elastomer 22 is thus radially stressed upon the skinned cable dielectric 1 becomes confined and stressed against the shell 8 at its bore 8 pressed between the glass annulus 24 and the inner end of the fastener 18, and also presses against the enlarged end of the ring 19.

The annulus 22 is a suitable elastic insulative substance and preferably is formed of a silicone compound known commercially as #916 Silastic rubber. This silicone material typically affords high resistance to compression set, and a heat resistance that is not detrimentally influenced range of ambient temperatures. typical physical properties, silicone rubber has not pretraverse of the direct and the reflected waves.

It was discovered that the physical characteristic measurements defining typical properties of the subject silion the cable 1.

cone compounds were based on tests upon non-stressed specimens. Such non-stressed test specimens were not restrained but, instead were free to assume differing dimensions due to volume expansion during increasing temperatures. It was conceived and experimentally verified that more favorable and practical results could be attained with a beneficial application of the silicone rubber when modified in a pre-stressed condition and operated in a compressed or deformed state directly in the traversing held of high radio frequency waves. This stressed and confined silicone elastomer affords surprisingly enhanced properties which give good effect to its application, not only as a pressure sealant but also as a wave transmission capacitance dielectric. This stressed elastomer is conlined and squeezed so that there is substantially uniform radial pressure between the coaxial conductors. It also combines with these conductors in a substantially discretely fixed diametrical ratio to afford a compensating capacitance per unit length, along the axis of the elastomer, with added utility for wave transmission. As the outer conductor dimensionally expands or shrinks under the influence of changing temperature, the inner conductor responds in a similar ratio. Meanwhile, at all times, the stressed elastomer remains confined and pressed against the temperature-changed conductors to maintain a predetermined working diametrical ratio.

The stressed capacitance elastorner additionally affords observed improvement as a sealant not only against passage of moisture and air but also in increasing the surface resistivity against creepage breakdown. The material behaves more favorably when pro-stressed and compressed than when it is in its free condition. If the solder 23 should melt during high temperature service conditions, the compressed elastomer 22 remains effective to hold the parts 1 and 10 in tight alignment so that the cable condoctor 1 nevertheless makes a good connection with the contactor 1h. The solder 23 is so held and connot be lost.

The novel combination of this stressed capacitance elastomer in the connector is not merely a substitution of one material for another suitable material. Instead, it affords a new combination wherein the operating properties of the compressed elastomer are favorably modified for the new purpose. The resulting deformation affords enhanced physical properties. These are surprisingly defined by a particular related dimensional utility attained by deformation in a diametrical discreteness along the length of the annular elastomer. The stressed elastomer is formed to present added utility with necessary characteristics that are not otherwise available.

It is intended that the shell sub-assembly of parts 8, 24, 25, 22 and nut 21 will normally remain permanently attached to the parts 18, 19 and that are sub-assembled When necessary, it is feasible to disassemble these parts or to connect a new length of cable in the same manner.

After the assembled contactor 10 is sealed or soldered to the guide ring 25, elastomer 9' is pressed and prestressed into the end of the shell 8 so that it extends beyond the end plug assembly 3 is removed from the receptacle 4. The annulus 9 is also made of a suitable flexible silicone rubber of commerce, but is always operated in a modified stressed condition that affords more favorable physical properties than for an unstressed or free elastomer. The dielectric ring 9 is also formed to have discretely differout working dimensions than the free dimensions. For a small fraction of the axial length along the elastorner 9 the outer diameter is increased. The inner diameters are reduced and the elastomer presses radially on the parts 25 and 10 and also, in the meshed position shown, upon a portion of the engaged contact pin 16 of the receptacle 4. Elastomer 9' is shown in its operating position axially compressed between glass annulus 24 and glass annulus 12 hermetically sealed within receptacle shell 13 of receptacle 4.

of the contactor 10 to protect it when the The threaded end 13,, of shell 13 is formed with an internally tapered bore 13 to align concentrically with the tapered end 8;; of the shell 8 so that the nut 21 functions selectively to draw these tapered surfaces together, or to release them. When shell- 8 is drawn upon shell 13, both shells effectively serve as a good noiseless electrical extension of the outer conductor 1 of the cable 1. The elastorner annulus 9 is squeezed to impermeably seal the annular compartment that is defined between the substantially parallel dielectric annuli 24 and 12, and the parts 25, 10, 16, 8 and 13. Shell 13 is preferably of a suitable metal such as #B-l113 steel. It carries the hermetically bonded glass seal in the form of an annulus 1.2, spaced away from the tapered bore end 13 This dielectric annulus 12 also concentrically carries a hermetically sealed contactor or pin 16, of a suitable metallic alloy, similar to the #52 nickel of the ring 25'. An enlarged bore 11 is provided in a capacitance dielectric elastomer 15 to afford impedance compensation adjacent the glass annulus 12.

After the annulus 12 is bonded and compression sealed to the shell 13 and the contactor 16, the exposed metallic surfaces of 13 and 16 are suitably plated to afford good electrical conductivityand corrosion resistance.

An impedance compensating metallic tube 16;, is carried in the pre-stressed silicone capacitance elastomer 15 and pressed over the contactor 16. The radially stressed capacitance elastomer 15 functions to maintain the contactor 16 and the sleeve 16 concentric with the bore 13 in the receptacle shell 4.

The shaped and externally threaded end 13;, of shell 13 is adapted for entry through a hole in a bulkhead or wall 6 of an electronic unit 6 and for fastening to the wall in any suitable way such as by means of a silicone or other suitable gasket 20 and a nut 14.

The working terminals of the unit 6 are not shown but are to be connected in a customary manner, as by soldering, to the end of parts -16 and 16,; while the shell 13 becomes electrically grounded to the bulkhead 6 The receptacle assembly 4 is intended to remain attached to the electronic unit, such as 6, but may also be detached for necessary repairs.

The overall axial length of an assembled connector set 2 comprising sub-assemblies 3 and 4 is preferably less than one fourth wave length and not more than one wave length, corresponding to the highest transmission frequency to be accommodated. For example, for high frequencies extending in the L-band of 390 to 1,550 me. and extending into the S-band of l,550 to 5,200 me. this axial length can suitably be approximately 1 inch. The individual lengths of the discretely dimensioned capacitance dielectric annuli 22, 24, 9, 12, 15 are kept as small as practicable and must each be less than one fourth wave length corresponding to the highest transmission frequency that traverses the connector set.

The cut cable 1 is effectively extended and sealed into the electronic unit 6 by this doubly hermetically sealed connector set 3, 4. Its inner conductor 1 has been extended into the unit 6 via the meshed contactors 10 and 16. Its outer conductor has been extended into the unit- 6 via the meshed annular shells 8 and 13. Its capacitance dielectric 1 has been extended via the coactin g sequence of discretely differing dielectric annuli 22, 24, 9, 12, 11 and 15. The connector set 2 fully withstands any ambient conditions in which cable 1 and unit 6 are usable. The dielectric'annuli also comprise combined impermeable seals for the cable 1 extended through the connector set 2.

The capacitance dielectric constants in the annuli 22, 24, 9,12 and 15 differ from the dielectric constant of the cables capacitance dielectric 1 and continue in a discrete sequence whereby the direct and the reflected waves have their velocity very slightly slowed down while traversing via said thin annuli. The particular dielectric constants for these capacitance annuli are preferably higher than that for the cables capacitance dielectric 1 and should at least be different so as to alter the phase velocity of the waves that traverse therethrough.

The velocity of wave propagation is the speed at which a particular phase of a transmitted or reflected waveform propagates itself in an axial direction along the coaxial line 5. For an air dielectric this would be nearly equal to the velocity of light. This specification discloses that the waves can be slowed down over a tiny distance which is less than one fourth of the wave length at the transmission frequency by combining very short tubular lengths of capacitance dielectrics having slightly differing diameters. Since the propagation velocity is simply the wave length multiplied by the frequency, it can be altered in quantity if either the inductance or the capacity is purposely made to aiford a diflerent relative value for a very short particular axial distance, because Velocity: (wave length) X (frequency) 1 35 v Inductance X Capacitance wherein D is the effective diameter of the outer conductor; d is the effective diameter of the inner concentric conductor; (Mu), the permeability, is herein unity (1.0).

For the same diameters ance in farads per meter is 0.241 *6 (In) C log lOD/d and axial length the capaciwherein:

e (epsilon) is the dielectric constant varies for dielectric materials other than air and may also vary for a particular material at different temperature).

For the same diametrical ratio of the conductors, the

diameter of one conductor can be changed if the diameter of the other conductor is changed accordingly.

Any discrete change in this diametrical ratio alters the inductance and the capacity along a particular axial distance where the changed diameters prevail. Any change in Epsilon does not affect the inductance over that same length, but does alter the capacitance.

The characteristic surge impedance of a coaxial line has a value in ohms expressed as follows:

wL; inductive reactance wC; capacitive reactance R+j L; ohms per meter i G+i C; ohms per meter I wherein:

10 R; high frequency resistance of the inner and outer conductors in series, in ohms per meter G; conductance (insulation loss of the dielectric material).

v Z0=\/ZW, (and per Equations II and III) band range of frequencies anywhere along the line. In Equation V it appears that the diametrical conductor ratio D/d and the dielectric constant, (Epsilon) e, uniquely determines the value of Z over any prevailing axial distance.

For discontinuities along the line, the prevailing value for Z over the changed axial line may be either higher or lower with the result that this circumstance may detrimentally influence the relative prominence of the direct and the reflected waves as respects the formation of standing waves. More particularly, this may increase the voltage standing wave ratio. Pulse waves propagated over such a non-uniform impedance line may be reflected in altered interfering waveform. Also for eflicient power transmission it is important to minimize the voltage standing wave ratio, that is, to reduce the reflected waves to a minimum.

In FIGURE 1, one of the units 7 can be considered as a wave generator and the other unit 6 can be considered to be a load for power transferred from 7 via transmission line 5. For no reflection, the load impedance at 6 should be exactly matched with the effective impedance Z of line 5. If there is any wave reflection due to a slight mismatch at the termination, the voltage and the current amplitudes of both the direct and the reflected waves will have a ratio at a particular point along value to the characteristic impedance Z According to the present disclosure the prevailing characteristic impedance over a small axial length can be modified for a particular diametrical ratio of the conductors over that distance by changing the value of the dielectric constant of the capacitance dielectric within that same distance. 0r both the diametrical ratio and the dielectric constant can be discretely altered over a fraction of that particular axial distance along the axis of the line so as to compensate effectively for inadvertent or necessary discrepancies which must be tolerated in the non-uniform continuity of a coaxial line, inclusive of its cut end and the connector therefor.

The very small dimensions of the conductors and insulation in a sub-miniature coaxial cable and its connecdiscontinuities required to be compensated. The preponderantly large effect of very small variations in accumulated tolerances become a large percentage relative to the tiny diameters that must be held in a constant diametrical ratio. It is preferable to hold to an average ratio rather than to very close tolerances on indivdual diameters. This is facilitated because the compressed dielectric annuli assume the same effective diameters defining the confining surfaces. Changes in the individual diameters of these confining surfaces occurring 1 1" during temperature variations also tend to conform to a fixed ratio to which the flexibly stressed elastomers readily adjust.

In FIGURE of the invention comprising fewer combined parts. Only two separable silicone capacitance dielectric elastomer annuli 27 and 28 operatively compressed together are employed in this embodiment of the invention. An annular shell 26 with a snap-ring 29 affords the essential functions previously stated in this specification relative to parts 8, 13 and 21. The receptacle shell 13 has a shoulder 13 and an annular extension 13 to engage and be soldered at 6 into the electronic unit bulkhead 6,, as indicated at 23 Printed circuit board pins .30 are also tightly fastened into the shell 13;; for the usual soldered connection to a printed circuit panel 6 comprised in unit 6. The shell 13 is intended to be permanently attached to unit 6. Pins 30 may be soldered to tubes 6 provided in panel 6 A body of silicone elastomer forming a capacitance dielectric member 28 is fitted tightly in shell 13 and has an enlarged elastic shoulder 28 shown stressed in FIG- URE 3. The capacitance dielectric member 28 tightly carries or is molded around the receptacle contactor 16 which is thereby held concentric with the inner bore of the annular shell 13 Shoulder 28 extends for a small fraction of the axial length of the dielectric member 28 to afford a higher impedance over only this fractional compressed length of the elastomer.

An internally shouldered nut 21 is held captive rotatably over annular shell 26 by a snap-ring 20 and affords a means to draw the externally tapered shell 26 against, or to force it away from, the interally tapered shell 13 The shell 26 is formed with stepped bores 26 26 and 26 which function like the bores 19 19 and 19 in the ring 19 of FIGURE 2, to engage the cable jacket and gather and bunch the loose cut ends ofthe outer Ring 29 is removably fitted in a groove 26, produced in shell 26. Similarly, shell 26 also is provided with another sequence of stepped bores 26 26 26 and 26,;, in which a flexible silicone capacitance dielectric ring 27 is fitted. The annular dielectric ring 27 has a bore 27 adapted to hold cont-actor 10 that is soldered to the cut end 1 of the inner conductor of cable 1. An opening 26;; is provided in a wall of shell 26 so that hot solder can be flowed through to secure the bunched cable conductor 1 In assembly, a bend relief sleeve 17 is first placed over the outer jacket of cable 1. Contactor 10 is soldered to the cut cable end 1 The sub-assembled parts 21 29, 26 and 27 are next turned and pressed over the contactor 10, the stripped cable end I and the cable jacket 1 The shell 26, after assembly on cable 1, is soldered to its bunched conductor 1 at the opening 26;; so that the solder electrically connects and secures shell 26 as an effective extension of the conductor 1 Sleeve -17 is then pushed over the end of shell 26 to cover the soldered connection, as shown.

As shown in FIGURE 3, shells 26 and 13 are meshed in good electrical contact and the inner meshed contactors and 16 are concentrically held by the radially stressed elastomer members 27 and 28. The insulating annuli 27 and 28 are squeezed and pressed together to form a sequence of discretely externally stepped portions of dielectric of differing diameters, when the nut 21 is tightened. Nut 21 also serves to press upon the ring 29 when it is to release elastomer 27 away from elastomer 28.

During disengagement of the connector each elastomer member 27 and 28 extends but remains radially stressed to respectively hold the unmeshed contactors 10 and 16 in axial alignment. The elastomer member 27 also remains stressed on the skinned cable end 1;; and protects the contactor 10 from damage. Contactor 16 has a groove 16 to engage elastomer 28.

cable conductor.

3 there is shown a simplified embodiment be used below 90,000

Nut 21 like nut 21 of FIGURE 2, has its engaged threads tightly held because of the spring bias action of the stressed elastomer members. This thread holding force is applied to the captive nut 21 via shell 26 from the squeezed elastomer shoulder 28 The species of the invention shown in FIGURE 3 may feet altitude to attain the same objectives as for the preferred form shown in FIGURE 2. It affords a tightly compressed seal for the cable end and its extension connector. The capacitance dielectric elastomers also operate in a favorably modified stressed con- 7 dition that affords added utility.

In both FIGURES 2 and 3 there is at least one elastomer, as 9 or 28, respectively, that has a discretely enlarged diameter for only a fraction along its axial length to provide a tightly compressed seal and to also afiord a discrete electrical impedance section of different value than along the remaining length of the dielectric elastomer.

The sequence of discretely different or higher and lower diametrical ratios for the capacitance dielectric that is shown in FIGURE 3 is modified from that of FIGURE 2 for the same functions but with the glass capacitance dielectrics omitted. Impedance is corrected in the same manner. The axial increment or length of the dielectric at each diameter is always less than that diameter. The combination shown in FIGURE 2 combines pressure sealing with fixed hermetic sealing to define a double hermetically sealed connector. The modification shown in FIGURE 3 also defines a pressure sealed connector but without the fixed glass hermetic seals. The telescopically engaged outer shells 26 and 13 are held concentric with respect the telescopically matinginner contactors l0 and 16 by the supporting action of the compressed elastomer members 27 and 2S.

This specification discloses a particular preferred species of an elastomer arranged to be physically modified by compression and deformation to particular dimensions surprisingly providing new and unexpected result with added utility. The specified relative dimensions for diameters over fractional lengths shorter than one quarter wave length of the highest transmitted frequency is not merely a dimensional change of usually expected consequences but rather defines a novel departure from the prior art affording a new and desirable result by compensating-for the discontinuity in the characteristic surge impedance and the reduced resistance to volt-age breakdown that is inherent where a cable is cut and extended.

Inasmuch as certain dimensions of the described coaxial cable connector are critical as respects the attainment of optimum results, it is desired to include in this specification by way of example only the dimensions and specifications of parts as listed below and found by actual Shell8:

Axial length 0.416 Axial length of bore 81: and 8 0.2703005 7 Axial length of bore 8 0.1603002 Diameter of bore 8 0.l60- *-.002 Diameter of bore 8 0.177-1005 Diameter of Main body of shell 8 0.2683005 O.D. of base of tapered portion of shell 8 0.2383002 CD. of small end of tapered portion of shell 8 0.2003002 Threads 8 specifications- 7 Tap, l2-28 NF-Z, 3 full threads. I Major, 0.2166 dia.; minor 0.1779" dia. (not plated).

1 Unplated pitch dia. 0.1940 to 0.1971. Seal assembly (shell 8; seal 24; seal collar 25; coin silver contact 10):

Axial length of seal 24- (#9010 Dow Corning compression glass) 0.062{ O.D. seal 24 0.160 Axial spacing of seal 24 larger end of shell 8 0.256 .Axial spacing of seal 24 smaller end of shell 8 0.098 Seal collar 25, #52 Driver Harris Alloy- ID. of seal collar 25 0.040

, CD. of contact 10 0.040 Tip contact 10 axial projection beyond small end of shell 8 0.010

Plug shell 13:

Axial length 0.463 Diameter of bore 13 0.1681002 Length of bore 13 0.273 Axial length of tapered bore 13 0.123

Smaller diameter of tapered bore 13 0.208%..002 Larger diameter of tapered bore 13 0.2363002 Specifications of threads 13 4 -32 NEF-2A (class 2A after plate)- Before plating dimensions:

Major diameter Pitch diameter 4 full threads minor diameter 02736-02730 Specifications of threads 13;; 4-32 NEF 2A (class 2A after plate)- Before plating dimensions:

Major diameter 02440-02940 Pitch diameter 02253-02284 Minor diameter 02111-02106 Six full threads Receptacle seal assembly (plug shell 3; seal 12; contactor 16):

Axial length of seal 12 (Dow Corning #9010 compression glass) 0.062 Diameter of seal 12 0.168 Axial spacing of seal 12 from small end of plug shell 3 0210:.005 Axial spacing of seal 12 from large end of plug shell 8 0.185- -.005 Length of contactor 16 0.433

Inner tip contactor 16 axial spacing from adjacent end of plug shell 8 0050:.015 Outer tip contactor 16 projection beyond smaller end plug shell 8 0.020

Insulator assembly 15, 16A:

Axial length of insulator 15 0.250

CD. of insulator 15 0.1723002 Axial depth of bore 11. 0.025 ID. of bore 11 0.100 CD. of sleeve 16A 0042:.002 ID. of sleeve 16A 0.020

Sleeve 16A has press fit in bore of insulator 15.

I claim:

l. A connector including a scalable plug detachably matable with a complementally shaped hermetically sealable receptacle to interconnect a coaxial cable and an electronic system, said connector comprising a first conducting annular threaded shell having an axial bore snugly receiving the cables jacket and also a tapered bore, a clamping ring seated in this tapered bore having a sequence of reduced inner diameters cooperating to gather and hold the cut ends of the cables outer conductor away from the cables cut inner conductor over a stripped longitudinal distance greater than the diameter of the capacitance dielectric of the cable, an extension contactor fastened to the cut inner conductor of the cable, a guide ring concentric of said contactor, a second conducting shell surrounding and threaded to said first threaded shell, -a dielectric annulus hermetically bonded to said second shell and to said guide ring, and a flexible dielectric annulus of elastomeric material held compressed on the stripped capacitance dielectric of the cable and confined between said clamping ring and said bonded dielectric annulus.

2. A separable connector for detachably securing a coaxial cable to an electronic system, comprising separable nesting tapered shells of conductive material, conductive means for securing said shells snugly nested together, dielectric annuli hermetically bonded one to each of said nesting shells, separable inter-engaged inner contactor-s concentrically carried by said annuli, a combined sealant and capacitance dielectric of silicone elastomer held compressed axially and radially thereof between said annuli, and means to attach and seal a cut end of a coaxial cable to one end of said connector to extend its outer conducting path by Way of said conducting shells and its inner conducting path by way of said inner contactors and its capacitance dielectric by way of the dielectric annuli and the compressed silicone elastomer in a substantially compensated characteristic impedance relationship.

3. A hermetically sealed separable coaxial transmission line connector comprising, a receptacle tightly sealed about coaxial contactors, a cooperating plug adapted to seat said contactors and to be locked separably to said receptacle, a rigid dielectric ring hermetically seated in and bonded to said receptacle and in pressurized encircling contact With one contactor, a rigid dielectric ring seated in and bonded to said plug, flexible dielectric elastomer held compressed between the said two dielectric rings and the engaged contactors in the assembled position of the plug and receptacle, and means to attach and seal the end of a coaxial cable to said receptacle with the inner and outer conductors of said cable in firm electrical contact with said contactors and with said receptacle, respectively, and exhibiting a substantially matched characteristic impedance through the connector substantially matched with the characteristic impedance of the associated coaxial transmission line.

4. A compact high efiiciency hermetically sealed separable connector for detachably connecting a coaxial cable to electronic equipment while substantially avoiding reflection of wave-signal energy, said connector comprising inter-engaged complementally shaped male and female metallic tubular shells including a nut ring for locking said shells tightly assembled, one of said shells having means for holding a coaxial cable end clamped concentrically thereto with the outer cable conductor in electrical contact with said one shell, said one shell also having a ring of rigid dielectric material sealed at its periphcry to the interior of said shell and supporting axially through its center a contactor conductor, said contactor conductor having a well opening axially into the opposite ends thereof, one of said Wells having a close sliding fit over the end of the center conductor of said coaxial cable and the other well being adapted to receive and seat the end of a second cont-actor conductor projecting axially through a second rigid dielectric ring, said second ring being sealed to the interior of the other of said shells intermediate the ends thereof, and rings of resilient dielectric material bearing against the opposite faces of said first mentioned rigid dielectric ring so dimensioned as to be compressed and to fill the space between said contactor conductors and said shells in the clamped assembled position of said connector components thereby to exclude air and moisture and holding the electrical conductors rigidly in concentric relation.

5. A separable connector as defined in claim 4 characterized in that said rings of resilient dielectric material are silicone elastomer and in that said shells, contactor conductors, said dielectric materials and the portions of said coaxial cable enclosed by said connector shells are so contoured and dimensioned that the characteristic impedance of said connector substantially matches the characteristic impedance of said cable.

6. That improvement in a hermetically sealed terminal fitting for coaxial cables which comprises a bushing adapted to have a close fit about a coaxial cable end having its successive components cut back in annular steps, the end of said bushing toward the cable end having a tapering well seating a corresponding tapering metallic clamping sleeve stepped on its interior complementally to the juxtaposed stepped portion of said cable and effective when pressed into said bushing well to clamp said cable to said bushing while leaving the center cable conductor and a short length of the surrounding insulation for the center conductor exposed beyond said sleeve, a second metallic sleeve having threads mating with threads on said bushing and adapted to be assembled to the end of the latter to enclose and protect the exposed end of said center conductor, said sleeve having a glass ring extending thereacross between the ends of the sleeve and hermetically sealed to said sleeve, said ring having a female contactor conductor extending through the axial center thereof adapted to receive and firmly seat the exposed end of the center cable conductor, and a ring of silicone elastomer held compressed between the interior surface of said glass ring and the juxtaposed axial end of said cable and of said terminal fitting thereby to exclude air and other fluids from contacting the terminal end of said cable and effective to hold the components in contact therewith accurately spaced concentrically of one another.

7. A terminal fitting as defined in claim 6 characterized in that said second sleeve and the glass ring sealed thereto have substantially the same coefficients of expansion 8. A terminal fitting as defined in claim 6 characterized in that the recited components thereof mutually cooperate with one another to exhibit a characteristic impedance matching the characteristic impedance of said coaxial cable.

9. A terminal fitting as defined in claim 6 characterized in that said second metallic sleeve has an exposed terminal end tapered to nest snugly in a similarly tapering well in the end of a mating fitting of an electronic system, and said fitting being further characterized in that said contactor conductor extending through said glass ring is provided in its outer end with a well adapted to receive and seat another electrical conductor.

whereby wide range temperature changes are ineffective to rupture the seal between said sleeve and glass ring.

10. A high etficiency separable connector for use in forming a junction fitting for coaxial cabling, said connector comprising a first and a second bushing spaced axially apart and adapted to be held rigidly joined in axial alignment and in electrical contact by a pair of concentrically related interengaging intermediate sleeves one of which sleeves threads'onto said first bushing and the other of which threads onto said second bushing, said first bushing having means for clamping the stepped end of a coaxial cable snugly therein, the inner one of said concentric sleeves having hermetically sealed between its opposite ends a dielectric ring supporting centrally thereof a contactor conductor matable with the center conductor of a coaxial circuit, said second bushing having hermetically sealed therewithin a dielectric ring supporting centrally thereof a second contactor conductor matable with said firstmentioned contactor conductor, and rings of silicone elastomer encircling juxtaposed portions of said contactor conductors and spaced one between said dielectric rings and one between said first bushing and said first mentioned dielectric ring, each of said silicone rings being placed in axial and radial compression by the tightening of said sleeves and as an incident to the assembly of the recited connector components.

References Cited in the file of this patent UNITED STATES PATENTS 2,296,766 Bruno Sept. 22, 1942 2,460,304 McGee et al Feb. 1, 1949 2,540,012 Salati Jan. 30, 1951 2,762,025 Melcher Sept. 4, 1956 2,785,384 Wickesser Mar. 12, 1957 2,860,316 Watters et a1 Nov. 11, 1958 2,870,420 Malek Jan. 20, 1959 FOREIGN PATENTS 716,844 Great Britain Oct. 13, 1954 

4. A COMPACT HIGH EFFICIENCY HERMETICALLY SEALED SEPARABLE CONNECTOR FOR DETACHABLY CONNECTING A COAXIAL CABLE TO ELECTRONIC EQUIPMENT WHILE SUBSTANTIALLY AVOIDING REFLECTION OF WAVE-SIGNAL ENERGY, SAID CONNECTOR COMPRISING INTER-ENGAGED COMPLEMENTALLY SHAPED MALE AND FEMALE METALLIC TUBULAR SHELLS INCLUDING A NUT RING FOR LOCKING SAID SHELLS TIGHTLY ASSEMBLED, ONE OF SAID SHELLS HAVING MEANS FOR HOLDING A COAXIAL CABLE END CLAMPED CONCENTRICALLY THERETO WITH THE OUTER CABLE CONDUCTOR IN ELECTRICAL CONTACT WITH SAID ONE SHELL, SAID ONE SHELL ALSO HAVING A RING OF RIGID DIELECTRIC MATERIAL SEALED AT ITS PERIPHERY TO THE INTERIOR OF SAID SHELL AND SUPPORTING AXIALLY THROUGH ITS CENTER A CONTACTOR CONDUCTOR, SAID CONTACTOR CONDUCTOR HAVING A WELL OPENING AXIALLY INTO THE OPPOSITE ENDS THEREOF, ONE OF SAID WELLS HAVING A CLOSE SLIDING FIT OVER THE END OF THE CENTER CONDUCTOR OF SAID COAXIAL CABLE AND THE OTHER WELL BEING ADAPTED TO RECEIVE AND SEAT THE END OF A SECOND CONTACTOR CONDUCTOR PROJECTING AXIALLY THROUGH A SECOND RIGID DIELECTRIC RING, SAID SECOND RING BEING SEALED TO THE INTERIOR OF THE OTHER OF SAID SHELLS INTERMEDIATE THE ENDS THEREOF, AND RINGS OF RESILIENT DIELECTRIC MATERIAL BEARING AGAINST THE OPPOSITE FACES OF SAID FIRST MENTIONED RIGID DIELECTRIC RING SO DIMENSIONED AS TO BE COMPRESSED AND TO FILL THE SPACE BETWEEN SAID CONTACTOR CONDUCTORS AND SAID SHELLS IN THE CLAMPED ASSEMBLED POSITION OF SAID CONNECTOR COMPONENTS THEREBY TO EXCLUDE AIR AND MOISTURE AND HOLDING THE ELECTRICAL CONDUCTORS RIGIDLY IN CONCENTRIC RELATION. 